Hydraulic couplers for quickly connecting and disconnecting attachments, such as buckets, from excavating and construction equipment are well known. Such attachments are usually attached to an arm of the excavator using two spaced and parallel pins provided on the attachment, wherein one of the pins is generally located in an open-mouthed substantially C-shaped aperture or recess of the coupling and the other pin is located in a similar C-shaped aperture or recess, one or both of the pins being secured within the respective C-shaped aperture by means of a movable jaw or latch member. The C-shaped apertures are arranged such that when the first pin is located in the first aperture and the second pin is secured in the second aperture and the or each latch member is closed the attachment is securely held by the coupling. Typically the or each moveable latch member is moved between an open and a closed position by means of a double acting hydraulic ram driven by a hydraulic circuit operated by a hydraulic control system.
When it is desired to remove, attach or replace an attachment from the arm of the excavator the arm is typically oriented so that the coupling is in a non-working orientation wherein that the bucket rests on the ground before the actuator is operated to move the or each latch member to its open position so that the arm can then be detached from the bucket. It is desirable to prevent opening of the latch member at any other time because release of the hydraulic coupling when in a working orientation while the attachment is suspended from the arm can cause the attachment to swing or even completely detach from the coupler, posing a serious safety hazard.
It is known to provide a gravity operated blocking member that is movable under the action of gravity between a first position, when the coupling is in its non-working orientation, permitting movement of the latch member from its closed to its open position, and a second position, when the coupling is in its working position, wherein movement of the latch member from its closed position is prevented by the blocking member. However, due to the conditions in which the excavator is used, such blocking members are prone to sticking or damage and may malfunction, allowing the latch member to move to its open position when the coupling is in its working orientation.